\[2,5;\ldots;20\]
\[b_{1} = 2,5;\ \ b_{4} = 20;\ \]
\[b_{4} = b_{1} \cdot q^{3}\]
\[2,5 \cdot q^{3} = 20\]
\[q^{3} = 20\ :2,5\]
\[q^{3} = 8\]
\[q = 2.\]
\[b_{2} = b_{1} \cdot q = 2,5 \cdot 2 = 5;\]
\[b_{3} = b_{2} \cdot q = 5 \cdot 2 = 10.\]
\[Ответ:числа\ 5\ и\ 10.\]